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The large range of motion afforded by the glenohumeral joint results in a propensity for instability.
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The constitutional trait of laxity facilitates extensive motion in multiple planes and may be essential to athletic performance.
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Range of motion and joint distractibility are increased in hyperlaxity, which is considered as instability when associated with loss of function.
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Strength and stability of the joint are highly dependent on both static and dynamic restraints.
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Soft tissue lesions associated
Functional Anatomy and Biomechanics of Shoulder Stability in the Athlete
Section snippets
Key points
What is instability?
The constitutional trait of hyperlaxity and the pathologic condition of instability represent distinct clinical entities.1 Laxity is the asymptomatic passive translation of the humeral head on the glenoid and may be essential to athletic performance. In hyperlaxity, this range of joint motion and joint distractibility are increased without loss of function. Glenohumeral instability is defined as excessive translation of the humeral head on the glenoid associated with a functional deficit.1
Normal shoulder stability
The balance between stability and mobility within the shoulder is achieved through complex interactions involving static and dynamic restraints.1 The bony static stabilizers include the glenoid, humeral head, and proximal humerus. The soft tissue passive stabilizers include the glenoid labrum, negative intra-articular pressure, articular cartilage surface, the glenohumeral ligaments, and the glenohumeral joint capsule. Soft tissue dynamic stabilizers are tendon-muscle complexes that provide
Classification of shoulder instability
The cause of shoulder instability is complex and multifactorial, and although several classification systems have been suggested, there is no all-encompassing system that adequately serves as a guide to treatment, predicts outcome, or facilitates communication between clinicians. Instability has been described in terms of direction (anterior, posterior, inferior, or multidirectional), degree of instability (dislocation, subluxation, or microinstability), chronology (acute, chronic, or acute on
Pathogenesis of instability in the athlete
Three broad etiologic categories have been implicated in instability of the shoulder: repetitive microtrauma to the shoulder, acute traumatic events, and purely atraumatic causes. It is crucial to identify the correct pathogenesis of instability so that treatment can be appropriately tailored to the patient’s needs.
Pathoanatomy of traumatic anterior instability
Traumatic anterior shoulder instability in the athlete usually occurs with a posteriorly directed force applied to the anterior aspect of an abducted, externally rotated arm. A direct blow (from posterior) can also cause a traumatic anterior dislocation. The humeral head is driven forward, producing a spectrum of soft tissue and bony lesions that are implicated in the pathogenesis of recurrent instability.
Pathoanatomy of traumatic posterior instability
The most frequent cause of recurrent posterior shoulder instability in the athlete is repetitive microtrauma to the posterior shoulder complex. In contrast to anterior instability, acute dislocation is usually not the most common initial presentation of posterior instability.50 A spectrum of soft tissue and bony pathologies is encountered, the nature of which depends on the cause of the instability.
Pathoanatomy of atraumatic instability
It is challenging to define atraumatic instability because activities of daily living and improper shoulder mechanics may lead to damage at a molecular level. Many athletes with evidence of constitutional ligamentous laxity develop unilateral instability only after a discrete injury; whilst some degree of inherited predisposition to traumatic instability is implied by its occurrence bilaterally in a quarter of patients.73 Atraumatic instability includes the diagnosis of multidirectional
Summary
Glenohumeral joint motion results from a complex interplay between static and dynamic stabilizers that require intricate balance and synchronicity. Instability of the shoulder is a commonly encountered problem in active populations, especially young athletes. The underlying pathoanatomy predisposing to further episodes and the needs of individual athletes must be considered in determining the most appropriate treatment.
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Postoperative MRI of Shoulder Instability
2022, Magnetic Resonance Imaging Clinics of North AmericaCitation Excerpt :Although first time acute dislocation occurs usually as the result of a significant traumatic event, such as a fall on an outstretched arm with the arm in abduction and external rotation, recurrent multiple shoulder dislocations can recur following more minor traumatic events. This in part is owing to chronic shoulder joint laxity and instability resulting from repetitive and chronic injury to the static and/or dynamic joint stabilizers or osseous injuries to the glenohumeral joint.2–4 Surgical treatment options for shoulder instability and postoperative outcomes depend on the accurate preoperative assessment of the patient, including the correct imaging characterization of the glenoid and humeral bone injuries.5–8
Humeral elevation reduces the dynamic control ratio of the shoulder muscles during internal rotation
2017, Journal of Science and Medicine in SportCitation Excerpt :The stability of the shoulder joint complex is largely dependent on dynamic contraction of the rotator cuff muscles.1–3 It has been suggested that changes in dynamic shoulder stability can contribute to shoulder injuries and pathologies such as shoulder impingement or instability.2–4 Pain in the shoulder region and accompanying impaired dynamic stability of the shoulder joint complex are typically noticeable during elevation of the upper arm and overhead activities such as tennis and volleyball serves when rotation of the humerus at the glenohumeral joint (GHJ) occurs.
Concurrent validity of handheld dynamometer measurements for scapular protraction strength
2019, Brazilian Journal of Physical TherapyCitation Excerpt :The shoulder is considered an unstable joint due to its anatomical features associated with a wide range of motion.1,2
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